The technology relates to a charging device for charging to a uniform potential a circumferential surface of a photoreceptor of an electrophotographic image forming apparatus.
Electrophotographic image forming apparatus include a photoreceptor and a charging device for charging a circumferential surface of the photoreceptor to a uniform potential. The charging device may be a noncontact charging device out of contact with the photoreceptor. The noncontact charging device includes an electrode. Application of high voltage to the electrode causes the electrode to discharge so as to charge the circumferential surface of the photoreceptor. A portion of the electrode that generates a high-voltage electric field attracts ambient dust. Large amounts of dust on the electrode prevent proper discharge thereof.
JP H11-338265A discloses a charging device that includes a needle electrode and a pair of pads. The electrode has a plurality of needles arrayed perpendicularly to a direction in which a circumferential surface of a photoreceptor moves. The pads are supported on both sides of the needle array of the electrode. Movement of the pads along the needle array brings the pads into contact with the needles in order so as to remove dust from the needles.
When the electrode is cleaned by reciprocating a cleaning member between a first end and a second end of the electrode along the surface of the photoreceptor, however, a high level of contamination of the electrode in an outward movement of the cleaning member requires a large driving load to be put on a drive source for moving the cleaning member. This reduces traveling speed of the cleaning member. In a homeward movement of the cleaning member, in contrast, the electrode has been cleaned and the level of contamination of the electrode becomes lower. Thus, a smaller driving load is required to be put on the drive source, and the traveling speed of the cleaning member becomes higher than in the outward movement. Therefore, supplying the same amount of power to the drive source in both of the outward and homeward movements causes the cleaning member to be moved at different speeds in the outward and homeward movements.
The conventional device includes a position sensor positioned near the first end. The cleaning member is reversed in a homeward direction after a predetermined time has elapsed since a point in time when the position sensor detects the cleaning member moving in an outward direction. According to levels of contamination of the electrode, this arrangement causes the cleaning member to be reversed from the outward direction to the homeward direction, or to be stopped, determined as having returned to the side of the first end, at an undesirable time.
This may cause the following problems. First, the cleaning member may be prevented from reaching an objective point near the second end in the outward movement, and thus portions of the electrode 2 may be left uncleaned. Second, the cleaning member may overshoot the second end in the outward movement and damage components of the device arranged near the second end. Third, the cleaning member may be prevented from reaching the first end in the homeward movement. Finally, the cleaning member may overshoot the first end in the homeward movement and damage components of the device arranged near the first end.
A feature of the technology is to provide a charging device that allows an electrode to be cleaned with a high efficiency while preventing damage to the device.